My invention relates to a motion translating mechanism for the convertion of bidirectional rotary motion into rectilinear reciprocation, and more specifically to such a mechanism of the type having a band of flexible, nonstretchable material looped about a pulley on a drive shaft, with the opposite end portions of the band extending substantially tangentially away from the pulley and attached to a member to be reciprocated rectilinearly. The motion translating mechanism of my invention lends itself to use as a transducer positioning mechanism in apparatus having a transducer for data transfer with a disklike record medium.
In data transfer apparatus employing magnetic disks, for example, a positioning mechanism is employed for incrementally transporting the transducer or magnetic read/write head radially of the disk in order to access each of a series of concentric storage tracks on the disk surface. The concept of using a band of stainless steel or like material for the transducer positioning mechanism is per se not new but is taught for example, by U.S. Pat. Nos. 3,881,189 to Mayeda and 4,161,004 to Dalziel. In such known positioning mechanisms the steel band is wound a single turn about a pulley on the armature shaft of an electric, bidirectional drive motor, with the opposite end portions of the band extending in opposite directions tangentially away from the pulley. The ends of the band are attached to spaced-apart positions on the carriage which carries the transducer and which is guided for linear travel in a radial direction of the magnetic disk. Such motion translating mechanisms have found a widespread acceptance in disk drives by virtue of the accuracy of positioning and the simplicity and inexpensive of construction with a minimum of moving parts.
As heretofore constructed, however, the positioning mechanisms employing the steel band have had one shortcoming in connection with means for imparting tension to the band, the band tension being essential for the accurate positioning of the transducer by the mechanism. The Dalziel patent suggests an example of such band-tensioning means, comprising a helical tension spring coupled to one of the two pivot arms to which are fastened the opposite ends of the flexible band. I object to this and other known band-tensioning means as they are not so simple in construction as can be desired.